database.yml generator. Global Rake implementation

dbconfig.rake

require 'yaml'

desc 'Generates database.yml, optional arguments: [adapter, user, password]'
task :dbconfig => 'database.yml'

file 'database.yml', [:adapter, :username, :password] do |t, args|
  Dir.chdir('config')
  args.with_defaults(:project_path => Dir.pwd)
  DBConfigGenerator.new(t, args).generate
end

class DBConfigGenerator
  ENVIRONMENTS = %w(production development test)
  DEFAULTS = {
    'adapter' => 'postgresql',
    'encoding' => 'unicode',
    'username' => Etc.getlogin,
    'pool' => 5,
    'password' => nil
  }

  def initialize(task, options = {})
    @database_pattern = "#{options[:project_path].pathmap('%-1d')}_%s"
    @template = {}
    @output_file = task.name
    @defaults = DEFAULTS.tap do |defaults|
                  defaults.each_key do |k|
                    defaults[k] = options[k] if options[k]
                  end
                end
  end

  def generate
    ENVIRONMENTS.each do |env|
      @template[env] = @defaults.merge('database' => @database_pattern % env)
    end

    File.write(@output_file, @template.to_yaml)
  end
end

Put this code into ~/.rake/dbconfig.rake file and you will be able to generate database.yml in any your rails project with this command: rake -g dbconfig. It won't regenerate the config again if it's already exists. So if you want to regenerate it you should delete it before.

Default options for each environment are:

adapter: postgresql
encoding: unicode
username: <current OS username>
pool: 5
password:
database: <project name>_<environment>

They may be changed though command line: rake -g "dbconfig[adapter, usr, pwd]"